The present invention relates to an electrical insulating oil obtained by processing a distillate from a thermal-cracked oil obtained in a thermal cracking process using a petrolic heavy residual oil as a starting material.
Recently, because of the exhaustion of petroleum resorces, heavier crude oils have come to be used, thus giving rise to an increasing tendency of the amount of heavy oils by-produced such as residual oils in distillations. These heavy residual oils are of less industrial value by reason of their high viscosities or high sulfur and metal contents.
On the other hand, such heavy residual oils can be utilized in thermal cracking processes typified by coking, which may be the only utilization mode of those oils. By the heavy residual oil coking process is obtained a liquid substance, i.e., thermal-cracked oils, as well as coke and gas. Usually, the thermal-cracked oil distillates are obtained in large amounts by the heavy residual oil coking process.
Since the cracked oil distillates thus obtained in large amounts contain large amounts of unsaturated compounds and aliphatic hydrocarbons and do not have a sufficiently high octane number, they have heretofore not been used directly as gasoline base stocks for automobiles, for which purpose they are required to be further subjected to a reforming treatment such as a fluid catalytic cracking. At most, the distillates have been used as mere fuels for boilers, etc. Therefore, how to utilize such large amounts of thermal-cracked oil distillates is becoming a subject of discussion in the industrial world.